The invention relates generally to fuel gauging systems for fuel tanks. More specifically, the invention relates to fuel gauging systems that use ultrasonic level sensors particularly suited for fuel tanks on aircraft.
Ultrasonic fuel level sensors for detecting surface levels of fuel in a tank are well known. These sensors operate using echo ranging in which an ultrasonic pulse on the order of 1 megahertz is emitted towards the liquid surface. The ultrasonic pulse is reflected at the fuel/air interface and returns towards the sensor in the form of an echo pulse. This echo pulse is then detected by the same or a different sensor. The detection sensor typically produces an output signal that corresponds to receipt of the echo. Thus, the round trip time from pulse emission to echo detection corresponds to the distance of the liquid surface from the sensors.
Aircraft fuel gauging systems usually require a large number of such fuel sensors in each tank based on the tank size, location, configuration, degree of accuracy required and possibly for safety redundancy. It is not unusual for a fuel tank to contain 10 or 20 such sensors. Not surprisingly, as the number of ultrasonic sensors increases, so does the complexity of control mechanisms used to interrogate the sensors. Therefore, ultrasonic fuel gauging apparatus commonly have depended on the use of microprocessor controllers and their attendant overhead software programming. However, such dedicated microprocessor based systems can either he expensive to design and maintain, or require complicated interface circuitry to a more powerful system controller. Software errors can also either lower reliability or become costly to locate and remove as system complexity and size increases.
There is a need, therefore, for a lower cost, simpler design for an ultrasonic fuel gauging system that can control a multisensor system without the need for a microprocessor and its attendant software.